Bioequivalence and Bioavailability Forum

Dear ElMaestro,

were did your graph come from?
The infamous PowerTOST package for R gives f.i. a sample size of 102 if target power is 80%, achieved power is 0.802180.
Reading the value from your graph seems higher.


Dear Nirav,

The power curve given by ElMaestro is for the conventional ABE test.
Since you have employed a partial replicate design I suppose that you aimed for going with scaled ABE or widened ABE acceptance limits. Concerning the sample size for this have a look at this thread and search the forum.

Of course your CV results does not allow you to go for scaled ABE because the Reference variability is <30% for both PK metrics. But only if you see these values as "carved in stone".
Given the fact that the CV is usually underestimated in small pilot's you have IMHO a fair chance to come out in the pivotal study with CV's >30%.
BTW: An upper 80% CL for an estimated CV = 28% from a study with 9 subjects (df=6 for a 3-sequence study) is 39.9%.
Thus I suggest you to go with 24-36 subjects in the pivotal study and cross your fingers .

The high point estimate obtained in your pilot study may of course decrease your chance to arrive at BE considerably. If you have reasons to see this as real, and not only by chance, the number of subjects must be much higher then above suggested.
A tangible number I can't give you because there is no elaborate method for sample size or power estimation for scaled ABE up to now, at least as far as I know.

If you don't believe in your chance to arrive at CV >30% and take your obtained point estimator of 1.15 as truth you have to go with above 100 subjects. A study with which much money can be earned, of course only if you find a sponsor who has that money in his big long pocket .